Telecommunications (telecom) systems are carrying increasing amounts of information, both in long distance networks as well as in metropolitan and local area networks (MAN/LAN). At present, data traffic is growing much faster than voice traffic, and includes high bandwidth video signals. In addition to the requirement for equipment to carry increasing amounts of telecom traffic there is a need to bring this information from the long distance networks to businesses and to locations where it can be distributed to residences over access networks.
The equipment, which has been developed to carry large amounts of telecom traffic, includes fiber optic transport equipment that can carry high-speed telecom traffic. The data rates on fiber optic systems can range from millions of bits per second (Mb/s) to billions of bits per second (Gb/s). In addition, multiple wavelengths of light can be carried on an optical fiber using Wavelength Division Multiplexing (WDM) techniques.
The use of optical fibers allows large amounts of telecom traffic to be transported over long distances. However, as one of ordinary skill in the art would recognize, it is impossible to have direct connections from each device sending data to each device receiving data. Moreover, some of the data being transmitted from a particular device may be intended for an intermediate point while other data is destined for a final point. Furthermore, the intermediate point may also wish to transmit data to the final point. The optical fibers provide a high-speed data stream (pipeline) upon which to transmit data traffic from a plurality of devices to a plurality of other devices.
Thus, telecom networks utilize network elements (NEs) that act as nodes in the transportation of data. The nodes may be nothing more than an intermediate point for data, may be a destination point for data, or may be a point where data is added to and removed from the data stream. NEs capable of providing this functionality, adding and removing traffic, are referred to as “add-drop” multiplexers (ADMs).
ADMs include multiple interface cards which receive high-speed data streams, create a time division multiplex (TDM) signal containing the multiple data streams, and route the time division multiplex signal to a cross-connect unit which can disassemble the data streams, remove or insert particular data streams, and send the signal to another interface card for transmission back into the networks. By aggregating the multiple data streams into a TDM data signal, the data rate of the TDM signal is by definition several times the rate of the maximum data rate supported by the interface cards.
Standardized interfaces and transmission hierarchies for telecom signals have been developed and include Pleisochronous Digital Hierarchy (PDH), Synchronous Digital Hierarchy (SDH), and Synchronous Optical Network (SONET). In addition to these telecom transport standards, standards have been developed for interconnecting businesses and computers within businesses. These Metropolitan and Local Area Network (MAN/LAN) standards include Ethernet, Gigabit Ethernet, Frame Relay, and Fiber Distributed Data Interface (FDDI). Other standards, such as Integrated Services Digital Network (ISDN) and Asynchronous Transfer Mode (ATM) have been developed for use at both levels.
A network circuit (NC) is the path that a data stream will follow in order to communicate with each device wishing to receive that data stream. The path includes the elements within a telecom network that are traversed by the data stream. That is, the NC consists of NEs and links between the NEs. Within each NE is a data circuit that defines which interface cards within the NE should receive the data. The links of network circuits are defined by VLANs so that one can differentiate multiple links between the same NEs. A spanning tree protocol is run on network circuits (often as identified by the VLAN) to prevent layer-2 forwarding loops from being created.
However, as more and more network circuits are created, the links of the network circuits will overlap. Thus, the likelihood of a network with an intersecting set of VLANs topology is likely. An intersecting set of VLANs topology is when different links within a network circuit are identified by partially intersecting virtual LANs (VLANs). This type of topology makes it difficult or impossible to run a standard spanning tree protocol in order to prevent layer-2 loops. Moreover, some NEs include internal links. The internal links may form a layer-2 loop if multiple links of a particular network circuit are connected to the NE.
For the forgoing reasons there is a need for a method and apparatus for preventing an intersecting set of VLANs network topology. There is also a need for blocking layer-2 forwarding loops for any network topology including loops internal to NEs.